U.S. patent number 4,814,952 [Application Number 07/134,927] was granted by the patent office on 1989-03-21 for lighting device for an oven capable of being acted upon by microwave energy, in particular a household oven.
This patent grant is currently assigned to Bosch-Siemens Hausgerate GmbH. Invention is credited to Gunter Hammerl.
United States Patent |
4,814,952 |
Hammerl |
March 21, 1989 |
Lighting device for an oven capable of being acted upon by
microwave energy, in particular a household oven
Abstract
An oven has a baking space wall at least partly defining a
closed baking chamber to be acted upon by microwave energy with a
given basic microwave frequency capable of being radiated into the
baking space with a given wavelength. A lighting device for the
oven includes a bulb holder, an incandescent bulb mounted on the
bulb holder and protruding freely into the baking space from the
baking space wall without electromagnetic shielding, and electrical
connection lines supplying the incandescent bulb with current from
outside the baking chamber. The incandescent bulb has a glass bulb,
incandescent filament holders of equal length extending
substantially, parallel and alongside one another, and an
incandescent filament disposed between ends of the incandescent
filament holders in the glass bulb. The filament has a longitudinal
extension within which all spacings between given points along the
incandescent filament are equivalent to a maximum of 10% of the
given wavelength.
Inventors: |
Hammerl; Gunter (Bad
Reichenhall, DE) |
Assignee: |
Bosch-Siemens Hausgerate GmbH
(Munchen, DE)
|
Family
ID: |
6316541 |
Appl.
No.: |
07/134,927 |
Filed: |
December 18, 1987 |
Foreign Application Priority Data
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|
|
|
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Dec 18, 1986 [DE] |
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3643364 |
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Current U.S.
Class: |
362/92; 313/271;
219/758 |
Current CPC
Class: |
H05B
6/6444 (20130101); H05B 6/806 (20130101); H05B
6/76 (20130101); F24C 15/008 (20130101) |
Current International
Class: |
F24C
15/00 (20060101); H05B 6/76 (20060101); F21V
033/00 () |
Field of
Search: |
;219/1.55R,1.55E,1.55D
;362/92,94,226 ;315/3,5,39 ;313/271,318 ;126/273R,375E,19R |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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3543078 |
November 1970 |
Steinhart et al. |
4254450 |
March 1981 |
White et al. |
4559585 |
December 1985 |
Almgren et al. |
|
Primary Examiner: Scott; Samuel
Assistant Examiner: Kamen; Noah
Attorney, Agent or Firm: Lerner; Herbert L. Greenberg;
Laurence A.
Claims
I claim:
1. In an oven having a baking space wall at least partly defining a
closed baking chamber to be acted upon by microwave energy with a
given basic microwave wavelength capable of being radiated into the
baking space with a given wavelength, the improvement comprising a
lighting device for the oven including a bulb holder, an
incandescent bulb mounted on said bulb holder and protruding freely
into the baking space from the baking space wall without
electromagnetic shielding, electrical connection lines supplying
said incandescent bulb with current from outside the baking
chamber, said incandescent bulb having a glass bulb, incandescent
filament holders of equal length extending substantially parallel
and alongside one another, and an incandescent filament disposed
between ends of said incandescent filament holders in said glass
bulb, said filament having a longitudinal extension within which
spacings between any two given points along said incandescent
filament are no more than 10% of the given microwave
wavelength.
2. Lighting device according to claim 1, wherein the baking space
wall, from which said incandescent bulb protrudes into the baking
space, is substantially flat.
3. Lighting device according to claim 1, wherein said incandescent
bulb is a low-voltage bulb having a connected load of a maximum of
30 volts.
4. Lighting device according to claim 3, wherein said incandescent
bulb is a low-voltage bulb having a connected load of 12 volts.
5. Lighting device according to claim 4, wherein said incandescent
bulb is a halogen lamp.
6. Lighting device according to claim 3, wherein said incandescent
bulb is a halogen lamp.
7. Lighting device according to claim 3, wherein said incandescent
filament holders of said incandescent bulb and given points along
said incandescent coil of said incandescent bulb are spaced apart
from one another by a maximum distance of 1/16 of the given basic
microwave frequency.
8. Lighting device according to claim 1, wherein said incandescent
bulb has a glass base, and said incandescent filament holders of
said incandescent bulb extend through said glass base in the form
of connection plug prongs.
9. Lighting device according to claim 8, wherein the baking space
wall has a side facing away from the baking space, the bulb holder
is disposed on the side of the baking space wall facing away from
the baking space, and said connection prongs of said incandescent
bulb are inserted through duct holes formed in the baking space
wall into said bulb holder.
10. Lighting device according to claim 1, wherein the baking space
wall is formed of metal and has a side facing the baking space,
said bulb holder is disposed on the side of the baking space wall
facing the baking space, said connection wires extend through duct
holes formed in the baking space wall, and said connection wires
have a shielding jacket being grounded to the metal baking space
wall.
11. Lighting device according to claim 1, including an
electromagnetic transformer through which said connection lines are
connected to a current supply.
12. Lighting device according to claim 1, including a glass hood
covering said incandescent bulb with respect to the baking space.
Description
BACKGROUND OF THE INVENTION
Description of the Related Art
The invention relates to a lighting device for an oven, in
particular a household oven, the closed baking chamber of which can
be acted upon by microwave energy, including an incandescent bulb
mounted on a bulb holder and supplied with current from outside the
baking chamber through electrical connection lines.
In microwave ovens or microwave stoves with or without additional
thermal heat sources, lighting devices having incandescent filament
bulbs are used for lighting the baking chamber. In such devices,
the bulbs are typically disposed on the wall of the baking chamber
in the vicinity of one of the side walls or the upper wall of the
baking chamber. As is well known in this connection, a relatively
large opening must be provided in the baking chamber wall, behind
which the lamp base of the lighting device is secured outside the
oven space. Special means must be made in this vicinity in order to
prevent the escape of microwaves through the openings. Furthermore,
the fact that the incandescent bulbs with the incandescent
filaments and incandescent filament holders thereof act as
receiving antennae for microwave energy radiated into the baking
space must also be taken into account. Among other effects, the
voltages induced in such lighting systems generate currents which
cause current to flow over the incandescent filaments. The
incandescent coils of prior art lighting devices can and are made
to become incandescent, solely due to the action of these currents.
If these currents are superimposed on the currents supplied for
purposes of continuous illumination, then the typical incandescent
bulbs which are used would be rapidly destroyed by the overload The
electromagnetic microwave field moves around within the baking
space, among other reasons for the sake of attaining the most
uniform possible exposure to microwaves in the baking chamber.
However, at least in the prior art lighting devices that are
exposed to microwave energy, this causes the incandescent bulb to
light up intermittently, which is annoying. For these reasons, it
is the usual practice to provide ways of preventing or at least of
reducing microwave energy from being radiated onto the incandescent
bulb of the lighting device. The most often used means of
protection shade the lighting device from the space acted upon by
microwave energy with a so-called perforated screen formed of metal
material. Since the incandescent bulbs should be accessible and
capable of being changed from inside the baking space, especially
in built-in appliances, the perforated screen must be detachably
secured on the baking space wall, which once again presents
problems in terms of microwave shielding. Furthermore, a particular
disadvantage is the fact that the perforated screen sharply reduces
the luminous efficiency. In order to adequately light the baking
space, correspondingly powerful bulbs must be used, which in turn
present additional problems because of their pronounced heat
buildup.
It has also already been proposed to shift the incandescent bulbs
back behind the baking space wall, and to form the socket shaft for
the incandescent bulb in the form of so-called microwave traps.
This structure once again meets with considerable difficulties in
practical utilization and the incandescent coil that is shifted out
of the baking space again leads to reduced luminous efficiency.
It is accordingly an object of the invention to provide a lighting
device for an oven capable of being acted upon by microwave energy,
in particular a household oven, which overcomes the
hereinafore-mentioned disadvantages of the heretofore-known devices
of this general type and which assures good illumination of a
baking space that is capable of being acted upon by microwave
energy without the above-described unfavorable secondary effects
resulting from the action of microwave properties.
SUMMARY OF THE INVENTION
With the foregoing and other objects in view there is provided, in
accordance with the invention, in an oven, especially a household
oven, having a baking space wall at least partly defining a closed
baking chamber to be acted upon by microwave energy with a given
basic microwave frequency capable of being radiated into the baking
space with a given wavelength, the improvement comprising a
lighting device for the oven including a bulb holder, an
incandescent bulb mounted on the bulb holder and protruding freely
into the baking space from the baking space wall without
electromagnetic shielding, electrical connection lines supplying
the incandescent bulb with current from outside the baking chamber,
the incandescent bulb having a glass bulb, incandescent filament
holders of equal length extending substantially parallel and
alongside one another, and an incandescent filament disposed
between ends of the incandescent filament holders in the glass
bulb, the filament having a longitudinal extension within which all
spacings between given, selected or arbitrary points along the
incandescent filament are equivalent to a maximum of 10% of the
given wavelength.
In accordance with another feature of the invention, the baking
space wall, from which the incandescent bulb protrudes into the
baking space, is substantially flat.
In accordance with a further feature of the invention, the
incandescent bulb is a low-voltage bulb having a connected load of
a maximum of 30 volts.
In accordance with an added feature of the invention, the
incandescent bulb is a low-voltage bulb having a connected load of
12 volts.
In accordance with an additional feature of the invention, the
incandescent bulb is a halogen lamp. This is done in order to
attain high luminous efficiency with small dimensions.
In accordance with yet another feature of the invention, the
incandescent filament holders of the incandescent bulb and given,
selected or arbitrary points along the incandescent coil of the
incandescent bulb are spaced apart from one another by a maximum
distance of 1/16 of the given basic microwave frequency.
In accordance with yet a further feature of the invention, the
incandescent bulb has a base or glass base, and the incandescent
filament holders of the incandescent bulb extend through the base
in the form of connection plug prongs.
In accordance with yet an added feature of the invention, the
baking space wall is formed of metal and has a side facing the
baking space, the bulb holder is disposed on the side of the baking
space wall facing the baking space, the connection wires extend
through duct holes formed in the baking space wall, and the
connection wires have a shielding jacket being grounded to the
metal baking space wall.
Typically and suitably, the supply of current to the incandescent
bulbs comes from a public utility grid with the corresponding
voltages, such as 220V. These voltages must be transformed for the
bulbs used in accordance with the invention which have lower
connected load voltages To this end, conventional transformers are
preferably used, having an intrinsic inductance which counteracts
the remaining slight energy absorbed by the incandescent bulb with
a practically infinitely high resistance. This prevents a more
extensive flow of current which could be returned by the microwave
radiation to the incandescent bulb located in the baking space,
through the connection lines for the incandescent bulb.
In accordance with yet an additional feature of the invention, the
baking space wall has a side facing away from the baking space, the
bulb holder is disposed on the side of the baking space wall facing
away from the baking space, and the connection prongs of the
incandescent bulb are inserted through duct holes formed in the
baking space wall into the bulb holder.
In accordance with again another feature of the invention, there is
provided an electromagnetic transformer through which the
connection lines are connected to a current supply.
In accordance with a concomitant feature of the invention, there is
provided a glass hood covering the incandescent bulb with respect
to the baking space. This is done on order to provide mechanical
protection against unintentionally touching and affecting the
lighting device.
By using an incandescent bulb in accordance with the features of
the invention and in particular in accordance with the features
further defining the invention, a lighting device is provided which
no longer presents any substantial problems with respect to the
microwave tightness of the baking space relative to the
surroundings thereof. The structure and dimensions of the
incandescent filament holders and the incandescent filament in
particular, insure that the antenna effect of the incandescent bulb
is negligibly small in terms of receiving the microwave energy
radiated into the microwave space. Since the resistances of the
incandescent filaments in bulbs having low connected load voltages
are also low, any currents induced in the bulb structure can be
compensated for without difficulty therein as well, without
disadvantageously affecting the incandescent filament. The ducts
passing through the baking space wall therefore need have only the
diameter of the shielded current supply connections, which does not
present any difficulties in terms of manufacture or of assuring
microwave tightness. The disposition of the incandescent bulb
inside the baking space without a metal shielding screen
surrounding it also has the advantage of making the total
illuminating force of the incandescent bulb available inside the
baking space. The connected power value for the incandescent bulbs
can thus be lowered and the power losses which have the effect of
dissipated heat, are reduced substantially as compared with
shielded bulbs. If halogen lamps are used, a bright white light is
furnished.
Other features which are considered as characteristic for the
invention are set forth in the appended claims.
Although the invention is illustrated and described herein as
embodied in a lighting device for an oven capable of being acted
upon by microwave energy, in particular a household oven, it is
nevertheless not intended to be limited to the details shown, since
various modifications and structural changes may be made therein
without departing from the spirit of the invention and within the
scope and range of equivalents of the claims
The construction and method of operation of the invention, however,
together with additional objects and advantages thereof will be
best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE FIGURES
FIGS. 1-3 are fragmentary, diagrammatic, cross-sectional views of
three different embodiments of lighting devices disposed on a wall
of a baking space and protruding into the baking space of a
household oven capable of being acted upon by microwave energy.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the figures of the drawings in detail and first,
particularly, to FIG. 1 thereof, there is seen a household oven
having a baking space or chamber 1 which is capable of being acted
upon by microwave energy and is surrounded on all sides by baking
space walls and a baking space door. The only part of the oven that
is shown in the drawing is the vicinity of a partial section of a
baking space wall 2 which is shown in section, in which the
lighting device for the baking space is disposed. A bulb holder 3
formed of electrically insulating material is secured to the
partial section of the baking wall 2. Connection lines 5 lead from
female plugs 4 of the bulb holder 3 to a current supply device,
which is a transformer 17. The connection lines 5 are surrounded by
insulation and protrude through duct openings 6 passing through the
baking space wall 2. The connection lines 5 have a metal shielding
jacket 7 in the vicinity of the duct openings 6 and adjacent
thereto, which also extends between the bulb holder 3 and the
baking space wall 2. The metal shielding jacket 7, grounded to the
metal baking space wall, prevents a major dissipation of microwave
energy out of the baking space 1 through the duct holes 6. In this
way, the required microwave tightness in this vicinity is
accordingly provided. An insulating tube 8 is slipped over each
metal shielding jacket 7.
Connection plug prongs 10 of a halogen lamp 11 inserted into the
female plugs 4 of the bulb holder 3. The connection prongs 10 are
extended through a glass base 12 of the halogen lamp 11 in the form
of incandescent filament holders 13, which are substantially
parallel to one another. A coiled incandescent filament 14 is
fastened between free ends of the incandescent filaments holders 13
inside the glass bulb of the halogen lamp 11.
The spacing between the connection plug prongs 10 and the
incandescent filament holders 13 amounts to approximately 4 mm,
while the length of the incandescent coil 14 amounts to
approximately 6 mm. The connection voltage for the halogen lamp is
12 volts. Since the halogen lamp 11 protrudes freely into the
baking space, a connection power of 5 watts can be sufficient.
The halogen lamp is covered with respect to the baking space 1 by a
glass hood 15, in order to protect the halogen lamp 11 from being
unintentionally touched and damaged.
The embodiments of FIGS. 2 and 3 vary in terms of the disposition
of bulb holders 3' and the incandescent bulb 11 relative to baking
space walls 2' and 2". The baking space walls 2' and 2" have
protrusions or bulges 16' and 16" in the vicinity of the bulbs and
the lamp holders which extend from the baking space 1. Glass hoods
15' and 15" are detachably secured by using conventional means in
the indentations of the baking space walls 2' and 2" formed by the
protrusions. In FIG. 2, the bulb holder 3' is disposed on the side
of the baking space wall 2' facing toward the baking space 1, and
in FIG. 3 it is disposed on the side of the baking space wall 2"
facing away from the baking space 1. In the FIG. 3 embodiment, the
connection prongs 10 of the incandescent bulb 11 protrude through
two holes 6" in the baking space wall 2" into the bulb holder 3".
The shield 7" is wrapped around the holder up to the baking space
wall 2".
* * * * *